Different problems and issues comes in Ubuntu time to time. The brightness problem in Ubuntu 12.04 and Ubuntu 12.10 in many laptops are common. For the brightness problem in Ubuntu 12.04, 12.10, 13.04 or other version you can go to this link( Increase and Decrease brightness in Ubuntu) and control the brightness.
But another problem of no backlight in Ubuntu 13.04 after opening from suspend or sleep is new for first time after installing Ubuntu 13.04. So, if the backlight problem had came to your Ubuntu version follow the instructions given below:
First one terminal (Clt+Alt+T) and execute the command given below:

sudo gedit /etc/pm/sleep.d/00-displayfix

Now copy and paste the code given below. Don't forget to save file after copying the file:

In my case I have to change the lineecho 500 > /sys/class/backlight/intel_backlight/brightnessinto echo 4 > /sys/class/backlight/toshiba/brightnessdue to hardware specification. Now it works! Thank you very muck!

Just a piece of advice prior to doing the procedure. Firstly you need to know what folder is inside /sys/class/backlight. Hence type:

ls /sys/class/backlight ----> This will give you the files inside. For me it was: acpi_video0. So, I complete answer for this one would be:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~cat /sys/class/backlight/acpi_video0/brightness --> shows current brightness level, say it returns 6gksudo gedit /etc/rc.local --> opens the file to be editedecho 6 > /sys/class/backlight/acpi_video0/brightness --> sets the desired level of brightness